The present invention relates to a radar apparatus.
In a conventional radar apparatus, an object around a transmitting station (for example, a ship) can be displayed on a screen. If the object is a fixed obstacle such as an island or land, a position of the transmitting station can be roughly measured based on a positional relationship between the fixed obstacle displayed on the radar apparatus and a transmitting point on the screen. As a method for measuring a position of a ship, LORAN, OMEGA and DECCA which utilize an electromagnetic wave emitted from a wireless station on a ground, and NNSS and GPS which utilize a satellite have been known.
However, in the measurement of the position of the ship by the conventional radar apparatus or LORAN, OMEGA or DECCA, the measurement data includes a relatively large error. Accordingly, if it is desired to move back the ship to a position which the ship has previously passed through, it is not actually possible to move back the ship to the exact position. In addition, since the position is digitally displayed, it is necessary to navigate the ship to the target point while tracing a locus on a chart. As a result, it takes a time to measure the position, and the determination of direction and distance of movement is delayed, and hence it takes a time to reach the target point. A special display device which can solve the above problems is available but it is very expensive and need an installation space.
And a device to superimpose a chart on a display disclosed by Tanaka in JP-A-57-131082 has an disadvantage for art, because it should bear image information of charts around any current location of the ship.